Rage, Rage Against The Dying Of The Light

Rage, rage against the dying of the light–Do not go gentle into that good night–Dylan Thomas

Stars do not live forever; they cast their lovely, glittering light into the merciless darkness of Space for a time, and then turn off like little candles lost in Eternity. Small, solitary stars, like our own Sun, die with relative peace and great beauty, puffing their outer layers off into the darkness of Space. When our solitary Sun dies, it will first swell up into a bloated Red Giant star, cannibalizing the inner planets Mercury, Venus, and possibly our Earth. It will then eventually wither into a very dense little stellar corpse termed a white dwarf, that will be surrounded by one of the most beautiful shrouds our Universe has to offer–a so-called planetary nebula, an enchanting “butterfly” of the Cosmos, made up of varicolored gases that once composed the outer layers of the now dead, small, lonely star.

More massive stars, however, blast the Universe with fire when they die spectacular supernova deaths. Supernovae are the most brilliant and powerful stellar explosions in the Universe, and they can be observed all the way out to the most remote corners of the Universe. Stars blast themselves to smithereens for two reasons–they have, vampire-like, sucked up too much mass from a sister-star and victim, or they have burned up their necessary supply of nuclear fuel that has kept them bouncy against the relentless force of gravity, and have dramatically collapsed, and then exploded, hurling starry-stuff into the Cosmos.

In February 2013, astronomers announced that it may be possible to forecast when a massive star will go supernova by observing the warning signs of the smaller bursts it releases just before it explodes in incandescent rage.

Star Death

Our Sun, at present, is a common place and relatively puny, main-sequence (hydrogen-burning) star. It is a beautiful, glittering golden-yellow. There are eight major planets, an assortment of primarily icy moons, and other smaller objects that compose our Sun’s familiar and enchanting family. Our Solar System dwells in the far suburbs of an ordinary, though majestic, barred spiral Galaxy, the Milky Way. Our Sun, like all stars, will die. But, today, it is a bouncy star, still in active and productive mid-life, lighting up the darkness that surrounds it with an incandescent fire. However, in another five billion years or so, it will be an elderly star, with little life left in the main-sequence. Stars of our Sun’s small mass usually live for about 10 billion years. But our Star, and middle-aged stars just like it, will go on blasting Space with light, burning hydrogen in their hearts by way of nuclear fusion, for another 5 billion years, or so.

When our Sun and other Sun-like stars have finally burned up their supply of hydrogen fuel, their looks start to change. They are now old stars. In the heart of an elderly Sun-like star, there is a hidden heart of helium, surrounded by a shell in which hydrogen is still being fused into helium. The shell begins to swell outward, and the hidden heart grows larger as the star ages. The helium heart itself begins to shrivel under its own mass, and it heats up wildly until, at last, it grows searing-hot enough at the center for a new stage of nuclear fusion to begin. Now it is the helium that is being burned to manufacture the heavier element, carbon. Five billion years from now, our dying old Sun will bear a small and extremely hot heart that will be emitting more energy than our still-active middle-aged Sun is at the moment. The outer layers of our Star, by this time, will have swollen up to ghastly proportions–it has become a glaring Red Giant star, hungry for the blood of its own planet-children! Ultimately, the core of our Star will continue to shrivel, and because it is no longer able to emit radiation by way of nuclear fusion, all further evolution will be determined by the force of gravity alone. Our angry, dying Star will hurl off its outer layers, but its heart will remain intact. All of the Sun’s matter will ultimately collapse into this pathetic remnant object that is only about the size of our small planet. In this way, our Star will evolve into the type of stellar corpse known as a White Dwarf. A White Dwarf star is doomed to become progressively colder and colder over time. In the end, our Sun will probably become an object known as a Black Dwarf. Black Dwarf stars are hypothetical objects because it is thought that none (as yet) dwell in our Cosmos. It takes hundreds of billions of years for a White Dwarf to ultimately cool down to the Black Dwarf stage, and our Universe is “only” a bit over 13.7 billion years old.

Stars that weigh more than at least 8 times that of our Sun, die with much more anger than their smaller counterparts. Massive stars cannot hold their own against the crushing property of gravity. Although the war between good and evil is often referred to as the oldest conflict, the war between pressure and gravity is considerably older. The pressure–which pushes everything out–is derived from nuclear fusion, and it is what keeps a star bouncy against the crushing force of gravity. Gravity seeks to pull everything in. When a star runs out of hydrogen fuel, and reaches the point where its pushing pressure can no longer hold its own against the pull of gravity, it has reached the end of the road. Supernovae usually pop-off when the iron core of a massive star reaches 1.4 times the mass of our Sun. The most massive stars in the Universe collapse and blow themselves out of existence altogether, becoming that gravitational monstrosity, a black hole. Massive stars, that are somewhat less massive, blow themselves up in supernova blasts, becoming a dense stellar corpse known as a Neutron Star. Neutron Stars are even more dense than White Dwarfs.

Forecasting The Storm

In a paper published in the February 7, 2013 issue of the journal Nature, an international team of astronomers suggests that it may be possible to predict when a star is ready to go supernova before it undergoes that final, deadly blast. One of the study’s authors, Dr. Mark Sullivan of the University of Southampton in England, explained in the February 8, 2013 Space.com that “For a star like our Sun, the energy it is emitting from the fusion of hydrogen into helium deep in the core exerts an outward pressure on the star, usually counteracted by an inward pressure from gravity. However, if the star’s luminosity increases above a certain amount–the so-called Eddington luminosity–the outward pressure from the resulting radiation is strong enough to overcome the gravity, which can then power an outflow of material. Gravity waves can act as a conduit to translate this large, super-Eddington luminosity in the core into an ejection of material from the outer envelope of the star.”

The team of astronomers used three telescopes in their endeavor to find out more about the way elderly stars rage before they die–NASA’s Swift mission, the Palomar Observatory, and the Very Large Array (VLA). The researchers began by studying a star dwelling about 500 million light-years away from our planet. The massive star weighed in with approximately 50 times the mass of our Sun, and it ultimately blasted itself to smithereens as a supernova dubbed SN 2010mc.

The astronomers’ study indicates that 40 days before that final, deadly explosion, the dying old star emitted a giant outburst, releasing matter that was equivalent to about 1 percent the mass of our Star–that is, approximately 3,330 times the mass of our planet–at about 4.5 million miles per hour.

This explosion radiated “about a million times more than the energy output of the Sun in an entire year,” Dr. Sullivan continued to explain. He added that this precursor nonetheless “is still about 5,000 times less than the energy output of the subsequent supernova.”

The close timing between the smaller outburst and the ultimate explosive end of the star suggest very strongly that they are related. One of the study’s authors, Dr. Mansi Kasliwal at the Carnegie Institution for Science in Pasadena, California, told the press in February 2013 that “What is surprising is the short time between the precursor eruption and the eventual supernova explosion; one month is an extremely tiny fraction of the 10-million-year lifespan of a star.”

The lead author of the new study, Dr. Eran Ofek of the Weizmann Institute of Science in Israel, noted in the February 8, 2013 Space.com that probability models showed that there was only a 0.1 percent chance that the outburst was a random event.

Comparing their data with three models proposed for explaining how the preceding outburst might have happened, the astronomers discovered that gravity waves helped drive mass to the star’s atmosphere. Gravity waves are fluctuations resulting from matter that is rising because of buoyancy, and then sinking because of gravity.

“Our discovery of SN 2010mc shows that we can mark the imminent death of a massive star. By predicting the explosion, we can catch it in the act,” Dr. Kasliwal continued to explain.

Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various newspapers, magazines, and journals. Although she has written on a variety of topics, she particularly loves writing about astronomy because it give her the opportunity to communicate to others the many wonders of her field. Her first book, “Wisps, Ashes, and Smoke,” will be published soon.